Hydraulic and hydrostatic units, such as fluid pumps and motors, typically contain internal passages for routing pressurized fluids among various locations within the unit. In order to service different components of the mechanical systems in which the units are employed, as well as for servicing the units themselves, it often is desirable to block a particular passage within the unit and seal the passage to restrict pressurized fluid from passing to other passages or fluid ports in the unit. Fluid seals are used to establish the desired sealing of a flow passage.
Once a fluid seal has been formed and flow is adequately diverted within the hydraulic or hydrostatic unit, servicing or testing of the unit can be completed without undesired fluid interfering with the work. When the work is completed, in order to return the unit to a fully operable condition, the seal must be removed such that the previously blocked passage is unobstructed and the fluid no longer is restricted. A permanent plug would render the unit incapable of performing its intended function.
Due to the rather complex fluid routes within a hydraulic or hydrostatic unit, it frequently is difficult to gain physical access to a particular location within a passage. To isolate two branch passages extending from a remote end of a main passage, for example, it is necessary to form a seal in the main passage between the two branches. Accordingly, the capability of positioning a seal with relative accuracy within a remote portion of a fluid passage is an additional important feature for a fluid seal of the character described.
One approach toward providing a fluid seal within a passageway has been to insert an expandable tubular plug sleeve into a passageway and subsequently force a hardened spherical element through the plug, such that the plug is deformed plastically to assume the shape of the passageway and form a suitable seal therein. Such an approach is disclosed in U.S. Pat. No. 3,058,431 to Eddy, in which bulges are formed on the outer surface of an expandable plug to interengage the sidewall of a valve body, and also in U.S. Pat. No. 3,825,146 to Hirmann, in which a tubular plug sleeve has sharp-edged teeth engaging the sidewalls of a workpiece bore.
While the above approaches provide a reasonable seal, significant problems lie in the fact that, due to the nature of the deformation of the plug elements, the seal becomes permanently fixed within the passage. Further, damage to the passage can result from the impact of the expanded plug. Substantial cost and effort is required to remove the plug, particularly when the seal is formed at a nearly inaccessible location. Also, because of the high force levels required to deform the sealing elements, a surplus of material can result in costly damage to the interior of the passage when the elements are expanded. Thus, these designs require that the geometric tolerances of the different components be precisely controlled, and require plugging systems of different sizes for use with different sizes of fluid passages.
Another proposed solution to the problem of providing a fluid seal has been to deform a spherical member within a passage. U.S. Pat. No. 3,522,648 to Weber discloses a sealing method in which a ductile aluminum sphere is deformed to create a metal-to-metal bond within a bore in a mechanical device. This design has the deficiencies described above with respect to the limitations of a permanent seal. U.S. Pat. No. 3,077,204 to Bennet illustrates one-way check valves formed by an elastic ball within a valve chamber. This type of stop cannot be variably positioned within a machine, and requires the manufacturing of dedicated bores within a machine to seat the balls.
There is a need for a fluid seal in a hydraulic or hydrostatic unit which can be positioned selectively within a fluid passage and which easily can be removed for subsequent operability of the fluid unit. The seal must be easy to install without posing a threat to the integrity of the fluid passage or the unit. The present invention is directed to satisfying this need and overcoming one or more of the above problems.